Hot metal-working tool



Patented "July 7, 1931 NETED STATES PATENT OFFICE PAUL BURTON PIERSOL, OF BEAVER FALLS, PENNSYLVANTA, ASSIGNOR TO THE BAB- COCK & WILCOX TUBE COMPANY, OF WEST" MAY'FIELI), PENNSYLVANIA, A COR- PORATION OF PENNSYLVANIA HOT METAL-WORKING TOOL No Drawing.

110 pressure, should most desirably be made of a metal which has to a high degree the qualities of toughness and wear-resistance at high temperatures, and which does not spall or break up or crack at the surface when the working film or layer is heated to a high temperature while the body remains at a much lower temperature, and does not scratch the metal being worked, and which is stable and undergoes substantially no'change in its desirable physical properties after long use in hot metal Working involving-successive beatings to high temperatures.

The tools of the present invention meet these requirements very fully, having greater resistance to Wear and shock than hot-metalworking tools as heretofore made. This has been found especially true of rolling mill plugs according to the invention.

Much difliculty has been experienced in obtaining plugs for plug-rolling hot tubes and billet guides for tube piercing mills which would satisfactorily withstand the severe service to which these tools are subjected. Plugs and guides according to the i present invention have been found much superior to the best plugs heretofore used, giving longer service and a better product.

Rolling mill plugs and other tools according to the present invention are made from an iron-chromium-nickel alloy containing such proportionate amounts of chromium, nickel and carbon that the alloy is a stable austenitic alloy containing an amount of carbon. in excess of the amount which can be held in solu' tion in the austenite, such excess carbon being in the form of hard carbide particles distributed in the boundaries between the austenite grains. The preferred chemical composition of the alloy for rolling mill plugs and piercing mill guides, orshoes, contains from 18 to Application filed November 10, 1928. Serial No. 318,600;

35 percent of chromium, from 4 to 20 percent of nickel, and from .75 to 1.75 percent of carbon, with the balance principally iron; provlded, however, that with the chromium in thelower range the proportion of nickel should be sufliciently more than at percent to make the alloy stably austenitic, and that with the chromium in the higher range the proportion of nickel should also be greater than 4 percent and sufficient to. keep the alloy from being brittle.

Small amounts of certain other constituents apparently do no harm, and in some cases may be desirable. Silicon up to 2 percenthas been found harmless, and apparently more than this might be used Without seriously affecting the properties of the alloy. The same may be said as to manganese up to 1 percent or. more. small amounts is harmless and has the advantage of reducing the grain size of the cast metal, and, as a further example, tungsten may also be present in small amounts Without harmful effect. The alloy will usually be found to contain small percentages of sul- P111111. and phosphorous. The presence of alumlnum in the alloy in any considerable amount has been found undesirable.

The following analyses are of alloys within the scope of the invention which have been found especially good for rolling mill plugs and piercing mill guides:

Per cent Per cent Per cent Per cent Chromium 23. 07 25. 87 33. 47 25. 23 10. 42 9. 94 10. 19 3. 99

The plugs and guides made from the above .alloys have been cast to shape and have usu- Vanadium in the grain size small and to discourage segregation of the carbide particles.

The cast alloy of which the tools are made comprises in effect a medium hard, tough matrix holding the distributed very hard carbide particles. The carbide particles s0 held in the tough matrix give the wear-resisting properties, and by keying the austenite grains aid in resisting deformation.

The greater the amount of the carbide particles, the greater is the wear resistance, but the amount desirable is limited by the necessary toughness of the alloy. This necessary toughness varies accordingto the shape and size of the tool and the service for which it is intended. A small section to be subjected to heavy shock or strain requires a smaller proportionate amount of the carbide particles, even though this is at some sacrifice to the wearing quality. Furthermore, the higher the nickel content, the less carbon will be needed, since nickel does not dissolve carbon, and, therefore, a greater proportion of the total amount of carbon in the alloy will be present in the form of the desirable carbide particles. The amount of carbon need not, however, be varied in proportion to the amount of nickel in the alloy. From somewhat extended experiments I have found that from .75 to 1.75 per cent.

of carbon has given the most satisfactory results.

The temperature of re-crystallization after -cold working of characteristic specimens of the alloy has been found to be below 450 F. This is much below the temperature to which surface portions of the tools become heated in their use in hot metal working. The metal is, therefore, self-adjusting in use, with the result that its valuable properties are maintained over long periods of use and the metal does not change or deteriorate because of strains or distortions due to mechanical working. The alloy will, however, harden if worked at temperatures below the recrystallization temperature. The alloy has 'not been foundto respond to heat treatment other than being a-nnealable by heating to its temperature of recrystallization so as to relieve it from strains'whlch may have resulted from cold working.

In making the alloy, it has been found most desirable to use an electric induction furnace, first melting the proper proportionate; amounts of iron and nickel, and then adding sufficient chromlum in the formof ferrochrome, chrome metal or alloy scrap.

When these ingredients are thoroughly melted, the temperature of the bath is raised somewhat to obtain proper casting tempera- 1 ture and silicon and manganese are added to insure de-oxidation, and the metal is poured and cast in the ordinary manner. The alloy may, however, be produced by other melting processes which give sufficient temperaat all temperatures down to below room tern:

perature, and remains so under the conditions of use in hot metal working, involving repeated heating even up to temperatures considerably in excess of 2000 F.

The tools of the invention are, as stated, characterized by toughness and wear resistance at high temperature. The alloy is of medium hardness, but retains its hardness up to a high temperature, losing very little of its hardness up to 1400 F., and apparently losing very little more up to considerably higher temperature. Its tensile strength is not remarkably high, although higher than the cast iron alloys which have heretofore been largely used for rolling mill plugs. It is only slightly ductile, is forgeableto only a slight degree, and is machineable, but only with difficulty, if the carbon is not over 1.5 percent. The alloy resists oxidation, no serious oxidation taking place at temperatures up to from 1500 to 2000 F., depending on the chromium and nickel content. Scale does not form, therefore, under the usual hot working conditions. The alloy is highly resistant to shock and deformation, and its physical properties do not change after long use in hot metal working.

The metal of which the tools according to the invention are made has to a marked degree stability as to both its structural characteristlcs and its physical properties, such stability being due, apparently, to its stable austenitic character, its l e-crystallization at low temperatures, and its resistance to oXida tion at high temperatures.

The fact that the surface of rolling mill plugs of the present invention may be ground or otherwise smoothed without harming the worklng qualities of the plug or interfering Wlth its use, is of very considerable importance 1n permitting the plugs to be made true to the required size, and in some cases to be refinished to a smaller size after becoming surface worn. Steel and cast iron plugs heretofore used cannot be used if the surface has been ground or otherwise smoothed.

What is claimed is:

1. A tool for working hot metal required to have high resistance to heat and shock and to wear resulting from rubbing contact with the hot metal under high pressure, made of iron-chromium-nickelalloy containing such proportionate amounts of chromium, nickel and carbon that the alloy is a stable austenitic alloy having hard carbide particles distributed in the boundaries between the austenite grains.

2. A tool for working hot metal required to have high resistance to heat and shock and to hEHG high resistance to heat and shock and to wear resulting from rubbing contact with the hot metal under high pressure, made of a ferrous alloy containing from 18 to 35 percent chromium, from 4: to 20 percent nickel, and from .75 to 1.75 percent of carbon, the amount of nickel being substantially greater than 4 percent when the amount of chromium approaches the lower or higher limit of the stated range.

4. A tool for working hot metal required to have high resistance to heat and shock and to wear resulting from rubbing contact with the hot metal under high pressure, made of a tough ferrous alloy containing approximately 23 percent chromium and 10 per cent nickel and sufficient carbon toprovide hard carblde particles distributed in the boundaries between the austenite grains in sufiicient quantity to give high wear resistance.

5. A tool for working hot metal required to have high resistance to heat and shock and to Wear resulting from rubbing contact with the hot metal under high pressure, made of an iron-chromium-nickel alloy containing carbon present in the form of hard carbide particles, which is stable as to both its structural characteristics and its physical properties under temperature variations up to approximately 2000 F.

6. A tool for working hot metal required to have high resistance to heat and shock and to wear resulting from rubbing contact with the hot metal under high pressure, made of an iron-chromium-nickel alloy containing carbon present the form of hard carbide particles, which has the quality of toughness to a high degree and is stable as 'to both its structural characteristics and its physical properties under temperature variations up to approximately 2000 F. v

7. A tool for working hot metal required to have high resistance to heat and shock and to wear resulting from rubbing contact with the hot metal under high pressure, made of, an iron-chromium-nickel alloy consisting of a medium hardstable austenitic matrix containing distributed carbide particles.

8. A tool for working hot metal required to have high resistance to heat and shock and to wear resulting from rubbing contact with the hot metal under high pressure, made of stable austenitic iron-chromiuni-nickel alloy which is tough and is wear-resistant at high temperatures and the temperature of recrystallization of which is substantially below the temperature to which surface portions of the tool become heated in use.

9. A tool for working hot metal required to have high resistance to heat and shock and to wear resulting from rubbing contact with the hot metal under high'pressure, made of a stable austenitic iron-chromium-nickel alloy having hard carbide particles distributed in the boundaries between the austenite grains, the temperature of re-crystallization of which is below 450 F.

10. A tool' for working hot metal required to have high resistance to heat and shock and to wear resulting from rubbing contact with the hot metal under high pressure, made of stable austenitic iron-chromium-nickel alloy, having hard carbide particles distributed in the austenite grains, and which is tough and highly resistant to shock and deformation, highly wear-resistant at high temperatures, retains its hardness at high temperatures, is substantially non-oxidizable at high temperatures, and the temperature. of re-crystallization of which is below 500 F.

11. A cast tool for working hot metal required to have high resistance to heat and shock and to wear resulting from rubbing contact with the hot metal under high pressure, made of iron-chromium-nickel alloy containing such proportionate amounts of chromium, nickel and carbon that the alloy is a stable austenitic alloy having hard carbide particles distributed between the boundaries of the austenite grains.

12. A cast and surface finished tool for working hot metal required to have high resistance to heat and shock and to wear resulting from rubbing contact with the hot alloy having hard carbide particles distributed between the boundariesof the austenite grains.

14. A cast and surface finished rolling mill plug. made of iron-chromium-nickel alloy containing such proportionate amounts o'f rhromium, nickel and carbon that the alloy is a stable austenitic alloy having hard carbide particles distributed between the boundaries of theaustenite grains. v

,15. A rolling mill plug, made of a ferrous alloy containing from 18 to 35 percent chromium, from 4 to 20 percent nickel, and from .75 to 1.75 percent carbon, the amount of nickel being substantially greater than 4 percent when the amount of chromium approaches the lower or higher limits of the stated range.

16. A castrolling mill plug, made of a ferrous alloy containing approximately 23 percent chromium, 10 percent nickel and 1 percent carbon.

17. A tool for use in a rolling mill and subjected in use to rubbing contact with hot metal passing through the mill, made of an iron-chromium-nickel alloy containing such proportionate amounts of'chromium, nickel and carbon that the alloy is a stable austenitic alloy having hard carbide particles distributed between the boundaries of the austenite grains.

18. A rolling mill guide, made of a ferrous alloy containing from 18 to percent chromium, from 4 to 20 percent nickel, and from .75 to 1.75 percent carbon, the amount of nickel being substantially greater than 4 percent when the amount of chromium approaches the lower or higher limits of the stated range.

19. A piercing mill guide, made of an ironchromium-nickel alloy' containing such proportionate amounts of chromium, nickel and carbon that the-alloy is a stable austenitic alloy having hard carbide particles distributed between the boundaries of the austenite grains.

20. A cast piercing mill guide, made of a ferrous alloy containing approximately 23 percent chromium, 10 percent nickel, and 1 percent carbon.

PAUL B. .PIERSOL. 

